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Sampling Techniques

RANDOM
General description which every item in population has non-zero probability of being selected
...
Need sampling frame: selection of
items within frame done by
random no
...
from
calc/comp/tables of random no
...
Sub-groups (“strata”)
2
...
Selection of items within each
stratum done by simple random
sampling
- If no
...
of
clusters
...
Starts with strata of population
2
...
These strata now called clusters
- Each cluster should be reasonably
representative of entire population
Method of choosing individuals from a
sampling frame
...
accidental patterns of the
recurring numbers eg
...


Investigation of parasite in puffin
population: impossible to do
simple random, so select no
...
at random eg
...
If items in sampling
frame numbers 1, 2, 3… chose
random starting point eg
...
as 38, 128, 238…

Sampling Techniques

NON-RANDOM
Sampling
Quota

Explanation
1
...
how many
males and how many females etc
...
Choice of who is sampled left to
interviewer
D: Non-random
Opportunity Used when circumstances make sample
readily available
...
criminals, where research will lead to
individual case studies instead of results
applied to whole population
A: Useful as initial pilot study
SelfThose involved volunteer to take
selecting
part/given choice to participate or
decline
- Can have self-selecting sample where
people volunteer to answer questions
D: If enough people decline survey might
affect results
D: Someone who accepts to take part
but refuses to answer some question:
form of self-selection and might bias

Example
Method often used by companies
employing people to carry out
opinion polls

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